The present invention relates to a method and apparatus for the flexible development of a data processing system such as a microcomputer system and also to a semiconductor integrated circuit for data processing. The present invention relates to effective technology to be applied to a development method of a single chip microcomputer system and further to a single chip microcomputer applied to the present method.
In a microcomputer system formed on a wiring substrate with a single chip microcomputer as a key component having a CPU (central processing unit) at the center and required peripheral circuits formed on one semiconductor substrate, an exclusive LSI, a programmable device such as a PAL (programmable array logic) or a PLD (programmable logic device), and a TTL circuit or the like are installed. This hardware is used for data storage and data communication and for motor drive control as well as display control corresponding to the control object. When such a microcomputer application system is developed, to change or debug the software program, the memory holding the program must be corrected. In a single chip microcomputer incorporating a memory being the object of correction or change converting the memory into EPROM and enabling its writing control based on signal control from the outside is disclosed in Japanese patent application laid-open No. 198667/1985.
When a microcomputer application system with an external logic constituted on the outside of the single chip microcomputer needs to be changed, a very complex and time consuming procedure is involved. If correction of the hardware becomes necessary attendant upon a change of the operation specification or function of the system midway through development, a change of the program of the programmable device such as the external logic and reconstruction of the LSI by change of a mask pattern in the case of a hardware constituted by a gate array and a further change of wiring pattern in the wiring substrate becomes necessary. Therefore, measuring the change of the operation specification and the function of the system midway through the development of the microcomputer application system is delayed.
On the other hand, as microcomputer application systems become multifunctional and are further miniaturized data processing LSI such as a single chip microcomputer with various sorts of peripheral functions being on-chip is apt to be increasingly applied. Corresponding to this, the single chip microcomputer incorporates various sorts of peripheral functions which can be constituted as an external memory or an external logic, such as an interface circuit, a timer counter, an input/output control circuit, a ROM for storing the control program and a subprocessor on one semiconductor substrate. However, since the peripheral function incorporated in such a single chip microcomputer particularly a logic functional portion in hardware is fixed conventionally, although the program memory converted into EPROM can change the software program, in order to change the logic function in hardware, design change of the single chip microcomputer as a whole and the change of the mask pattern for the manufacturing must be performed, thereby existence of a problem has been made clear. Specifically, a user of the single chip microcomputer cannot himself set or change the operation specification or the function required in the logic functional portion in the hardware. Further, when the system having such single chip microcomputer as the key component is constituted even if only a partial change of the operation specification and the function of the system becomes necessary, the function of the single chip microcomputer cannot be dealt with flexibly and rapidly in response to the requirement. This problem also suppresses the multifunctional conversion of the single chip microcomputer.